<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		  <style>
        * {
            padding: 0;
            margin: 0;
        }
        .site-nav {
            height: 30px;
            background-color: #ccc;
        }
        .top-banner {
            background-color: blue;
        }
        .w {
            width: 1210px;
            height: 80px;
            background-color: pink;
            margin: 0 auto;
            position: relative;
        }
        .search {
            width: 1210px;
            height: 80px;
            background-color: red;
            margin: 0 auto;
        }
        a {
            position: absolute;
            top: 10px;
            right: 10px;
            width: 25px;
            height: 25px;
            text-align: center;
            line-height: 25px;
            background-color: #000;
            color: #fff;
            text-decoration: none
        }
    </style>
	</head>
	<body>
	<div class="site-nav"></div>
    <div class="top-banner" style="opacity: 1">
        <div class="w">
            <a href="#">×</a>
        </div>
    </div>
    <div class="search">
	</body>
	<script>
		//需求：点击关闭按钮，先让top-banner 这个盒子透明的变为0
		var topBanner=document.getElementsByClassName("top-banner")[0];
		var w=document.getElementsByClassName("w")[0];
		w.onclick=function(){
			var timer=setInterval(function(){
				topBanner.style.opacity-=0.1;
				if(topBanner.style.opacity<0){
						topBanner.style.display="none";
						clearInterval(timer)
				}
			
			},100)
			
		}
	</script>
</html>
